I. Field of the Invention
The present invention relates generally to antennas. More specifically, the present invention relates to a balanced, retractable dipole antenna for mobile phones.
II. Description of the Related Art
Recent advancements in electronics have significantly improved the performance of mobile phones. For example, advancements in integrated circuit technology have led to high performance radio frequency (RF) circuits. The RF circuits are used to construct transmitters, receivers and other signal processing components typically found in mobile phones. Also, advancements in integrated circuit technology have led to a reduction in the size of RF circuits, thereby leading to a reduction in the overall size of a mobile phone.
Similarly, advancements in battery technology have resulted in smaller, lighter and longer lasting batteries used in mobile phones. These advancements have resulted in smaller and lighter mobile phones that operate for a longer period of time on a single charge.
Generally, a user of a mobile phone must be able to communicate with another user or a ground station that can be located in any direction from the user. For this reason, the antenna in the user's mobile phone must be able to receive and transmit signals from and in all directions. Consequently, it is desirable that the antenna exhibit a symmetric radiation pattern having a uniform gain in the azimuth. In addition, it is desirable for mobile phones to have antennas that are retractable.
Unfortunately, antennas found in today's typical mobile phones do not exhibit a symmetric radiation pattern. Mobile phones generally utilize monopole antennas (for example, a whip antenna) that, due to the presence of unbalanced currents, exhibit asymmetric radiation patterns. This is primarily due to the fact that the shape and dimension of a monopole are not equivalent to to the shape and dimension of a ground plane of a printed wire board (PWB) used as a counterpoise, resulting in an unequal current distribution in the monopole and in the ground plane.
As a result, it has been recognized that there is a need for an antenna for a mobile phone that exhibits a symmetric radiation pattern.